It’s a common Hollywood aphorism that movies are made in the editing room. In the case of last year’s stealth box-office hit Wonder, though, you might say that it was a movie made in the makeup chair. That’s because the success or failure of the cinematic version of R.J. Palacio’s beloved bestseller hinged on whether special effects makeup artist Arjen Tuiten could convincingly transform the film’s 9-year-old star, Jacob Tremblay, into 10-year-old Auggie Pullman, a boy living with Treacher Collins syndrome, a genetic disorder that results in severe cranial and facial deformities. “It’s the hardest type of makeup to do, because it has to be believable even for viewers not familiar with Treacher Collins,” explains Tuiten, whose pre-Wonder credits include such fantastical fare as Maleficent and Pan’s Labyrinth. “If the makeup is distracting or mask-y looking, the movie wouldn’t work, because you’d just be staring at it.”

In other words, a lot was riding on Tremblay’s first session in Tuiten’s makeup chair, a pivotal moment that the young actor’s parents, as well as Wonder writer-director Stephen Chbosky, were present for as well. As the artist remembers, that was the day that the first tears for what became one last fall’s biggest tearjerkers were shed. “Both Jacob’s mother and Stephen cried after that first makeup test. We had things to refine still, but you could see it was going to work.” In a separate interview, the now 11-year-old Tremblay also remembers being awed by staring into the mirror and seeing a different boy gazing back. “I was like, ‘Wow, this looks really realistic!’ It helped me become Auggie; I wouldn’t have been able to play him without Arjen.”

Watch Tremblay’s transformation:

And Tremblay intends to fully (and loudly) express his gratitude on Oscar night should his collaborator take home the statue for Best Makeup and Hairstyling. It’s Tuiten’s first-ever nomination, and pits him against the trio of artists responsible for transforming Gary Oldman into Winston Churchill in Darkest Hour, as well as the team that refashioned Judi Dench into Queen Victoria in Victoria & Abdul. “I’m going to cheer him on,” Tremblay proclaims. “I think he definitely deserves it; it’s really amazing what he did. I like to say he made the body of Auggie and I’m the soul.” Not surprisingly, Tuiten has an equally high opinion of his young subject. “He’s a very old soul in that little body. It’s hard for any actor to go through [the makeup process], let alone a boy his age. I was very, very impressed.”

In addition to their work together in the makeup chair, both Tremblay and Tuiten independently researched Treacher Collins syndrome to enhance the realism of the Jacob-to-Auggie transformation. The actor solicited letters from families of Treacher Collins patients to understand the emotional experience of living with the disorder, while the artist sought information and reference material from medical professionals to better build Auggie’s face. As he learned, children with Treacher Collins tend to have similar distinguishing features — including drooping eyes, a sloped neck and disfigured ears — that can vary in terms of severity. “In the book, Auggie’s condition is a lot more severe, but in the film, we had to balance whether Jacob could act in [the makeup], does it look believable and can we still tell the story. We went through three different sculptures with very subtle changes; the neck needed to be a little more slooped, the hair needed to be a little shorter — stuff like that.”

Tremblay and Wonder author R.J. Palacio on the set of the film. (Photo: Dale Robinette/Lionsgate/Courtesy Everett Collection)

Once he had a sculpture he was satisfied with, Tuiten had to find a way of placing it on Tremblay in a time-efficient manner. Because of his age, Tremblay’s on-set availability was capped at nine hours and an intricate makeup job like this would typically eat up almost half of that allotted time. So Tuiten constructed a custom headpiece that could be built on top of Tremblay’s face in a mere 90 minutes. “Jacob is wearing a carbon-fiber skullcap with a wire system connected to it. That skullcap also doubled as his bald cap, so we skipped that part. His hair would get combed back, and then the skull cap would go over his head. His [false] ears were also permanently attached to that, because it would have added another 20 minutes to put them on separately. Then we had a whole neck, chin and cheek piece with a chest that would slide over his head, as well as contact lenses and false teeth. So Jacob is completely covered in prosthetics; it’s one of the first times in film history where a 9-year-old has been in a lead role wearing full prosthetics.”

Asked which part of his transformation impressed him the most, Tremblay points to Auggie’s drooping eye. “There was a mechanism connected to my lower eyelid, which pulled it down. They’d release it between takes, because if I had it down for too long, it would sting.” Of course, any minor stinging was preferable to the alternative, which would have been gluing the actor’s eyelid into a drooped position for multiple hours. As it was, Tremblay’s patience with the makeup process already had a time limit, specifically the amount of time it took him to stream a 90-minute narrative feature or documentary on his iPad. “He was very good for sitting still for that hour and a half,” Tuiten says, chuckling. “After that, he was done and wanted to run around.”

Patience is something that’s acquired with age, of course, so should Tremblay reprise the role for a Wonder sequel — an unlikely prospect, as Palacio has repeatedly said that she doesn’t intend to continue Auggie’s story into adolescence and adulthood — he’d likely be able to endure more than 90 minutes in the makeup chair. “I think it would be pretty cool if Auggie went to college; he loves space, so maybe he’s going to be an astronaut,” he says, excitedly. Should his pitch for Wonder 2 become a reality, though, his personal preference would be to see the role go to an actor who actually has Treacher Collins syndrome. (Funnily enough, Tuiten says that after the film hit theaters last fall, he received several notes from doctors who thought Tremblay was a real Treacher Collins patient.)

In the meantime, Tremblay is leaving the extensive prosthetics to his grownup co-stars, like the adult playing a certain intergalactic trophy hunter in The Predator, Shane Black’s upcoming reboot of that dormant franchise. Due in theaters on Sept. 14, the movie casts Tremblay as the son of star Boyd Holbrook, whose commando becomes the latest human solider to test his mettle against the Predator species. “It was such a fun set to be on,” he raves, carefully avoiding any details that might spoil the experience for moviegoers. But he can confirm that he had an up close and personal encounter with the Predator — a movie monster created by Stan Winston and brought to life again by noted Xenomorph expert Tom Woodruff Jr. — during shooting. “He’s huge! And his mouth is really gross. It’s cool-looking.”

Wonder is currently available to rent or purchase on Amazon, Google Play, iTunes and Vudu.